Electric arc furnace (EAF) technology is becoming an increasingly more important means for steel production world-wide. EAF technology, however, suffers from the disadvantage of producing, as a by-product, large quantities of EAF dust. Approximately 15 to 20 kg of EAF dust is formed per tonne of steel, meaning that millions of tonnes of EAF dust are produced annually world-wide. It is considered a toxic waste and its safe disposal is accordingly problematic. In some jurisdictions, landfill or like disposal of EAF dust is prohibited and so there is a significant incentive to process the dust into components able to be recycled or otherwise safely disposed of. Moreover, given that EAF dust includes as major components iron and zinc, and as lesser components lead and other elements of economic significance, it is a potentially valuable resource yet to be adequately commercially exploited. Zinc in particular may be usefully recycled to a variety of uses depending on the purity of the grade able to be extracted.
European patent publication 174641 is directed to the recovery of zinc and iron from EAF dusts. The disclosed process involves pelletising the dust with coke as a solid carbonaceous material, preheating the pellets in a shaft furnace, and thereafter transferring the preheated pellets, with additional reductant, to an induction furnace in which the pellets are melted. Zinc and lead are recovered as vapour from the induction furnace and condensed to crude zinc and lead metal, while pig iron and lead are separated out as molten phases in the induction furnace.
European patent publication 745692 is also concerned with zinc recovery but from a wide variety of dusts including EAF dust. The essential focus is again reduction, vaporisation, and condensation of the zinc or lead, but here there is no pelletisation or separate preheating stage. The treatment furnace is under a substantial vacuum, and the treatment is at around 750° C., i.e. well below the iron melting temperature but sufficient to vaporise the zinc.
In the process disclosed in international patent publication WO 91/09977 zinc vapour is recovered from a melt furnace in which EAF dust is melted in a proportional mixture of the dust, coal as a carbonaceous material reductant, and a slag forming flux agent. The zinc vapour is condensed to form zinc metal.
Australian patent 703821 discloses a process for reducing metal oxide fines and producing metal therefrom in which the fines are pelletised in a composite with a carbonaceous material such as brown coal or peat, preheated in a reducing atmosphere to reduce the metal oxide, and then, in a separate chamber, treating the reduced material to produce a molten metal containing phase. Retort apparatus suitable for carrying out this process is disclosed in international patent publication WO 01/38455.
There is clearly a need for an effective and safe means for dealing with EAF dust which also realizes at least a portion of its potentially extractable value.